Cleaning agent for dental use comprising a combination of polishing agents based on a silicic acid and aluminum oxide

ABSTRACT

A dentifrice in the form of an aqueous paste or liquid dispersion, comprising 10% to 30% by weight of a combination of silica polishing agents and aluminum oxide in a ratio by weight of 10:0.2 to 10:2, 20% to 50% by weight of a humectant selected from the group consisting of sorbitol, glycerol, 1,2-propylene glycol, and mixtures thereof, and 2% to 12% by weight of a condensed phosphate selected from the group consisting of tripolyphosphate, pyrophosphate, trimetaphosphate, and mixtures thereof. The condensed phosphates are in the form of an alkali metal or ammonium salt.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is a national stage application under 35 U.S.C. §371 ofinternational application PCT/EP98/05632 filed on Sep. 5, 1998, theinternational application not being published in English.

BACKGROUND OF THE INVENTION

This invention relates to a dentifrice in the form of awater-containing, paste-form or liquid cream containing 10 to 30% byweight of a combination of polishing agents and 20 to 50% by weight of ahumectant,of which the cleaning performance has been further improved byan addition of condensed phosphates

Toothpastes are used in the daily cleaning of teeth by brushing with atoothbrush. Toothpastes are intended above all to support the removalfrom the tooth surfaces of food remains, discoloration, for example bytobacco or tea, and firmly adhering bacterial films, so-called plaque.This is mainly done by the polishing agents present in the toothpasteand, to a lesser extent, also by the surfactants present. In order todevelop their cleaning and polishing effect, the polishing agents haveto have a certain abrasiveness towards the tooth surface. However, it isextremely important that the abrasiveness towards dental enamel anddentin is kept at low levels to avoid damage to the tooth surface by thedaily use of the toothpastes. Above all, the polishing agents usedshould not cause any deep scratches on the tooth surface. On thecontrary, they should have a smoothing effect on any roughness presentin the tooth surface.

Condensed phosphates are known from numerous publications as scaleinhibitors and as demineralization inhibitors in dentifrices.

The cleaning effect of water-soluble pyrophosphate salts on teethdiscolored by tea and coffee is also known from U.S. Pat. No. 4,822,599A.

Dentifrices containing an abrasive mixture of a silica polishing agentand a calcined aluminium oxide are known as particularly effective toothcleaning preparations from DE 27 58 548 C2. This document recommends theaddition of certain inorganic electrolyte salts to prevent abrasion ofthe dental enamel. In spite of this, extremely high dentin abrasionvalues (RDA) and enamel abrasion values (REA) of 300 to 500 wereobtained.

Although the abrasion values can be reduced by reducing or omitting thealuminium oxide polishing agent, cleaning performance is significantlyimpaired at the same time. Accordingly, there was a need to develop adentifrice which would combine very low abrasiveness (RDA and REA valuesbelow 100) with a very good cleaning effect (CRS values of around 100).

DE 34 25 152 describes a combination of polishing agents consisting of asilica polishing agent and a lightly calcined aluminium oxide with whichreduced abrasiveness can be combined with a good cleaning effect.

It has now been found that condensed phosphates are ideally suitable forincreasing the cleaning performance of toothpastes containing acombination of silica polishing agents and aluminium oxide polishingagents to such an extent that the need stated above is satisfied withoutany significant increase in the abrasion values.

Accordingly, the present invention relates to dentifrices in the form ofwater-containing, paste-form or liquid dispersions containing 10 to 30%by weight of a combination of silica polishing agents and aluminiumoxide in a ratio by weight of 10:(0.2-2) and 20 to 50% by weight of ahumectant from the group consisting of sorbitol, glycerol, 1,2-propyleneglycol or mixtures thereof, characterized in that they contain acondensed phosphate from the group consisting of tripolyphosphate,pyrophosphate, trimetaphosphate or mixtures thereof in the form of thealkali metal or ammonium salts in a quantity of 2 to 12% by weight inorder to increase the cleaning effect.

Suitable silica polishing agents are, for example, silica gels which areobtained by reacting sodium silicate solutions with strong aqueousmineral acids to form a hydrosol, ageing the hydrosol to form thehydrogel, washing and drying. If drying is carried out under moderateconditions to water contents of 15 to 35% by weight, so-called hydrogelsilicas, which are known for example from U.S. Pat. No. 4,153,680, areobtained.

Drying to water contents below 15% by weight results in irreversibleshrinkage of the previously loose structure of the hydrogel to the densestructure of the so-called xerogel. Xerogel silicas are described, forexample, in U.S. 3,538,230.

A second preferred group of silica polishing agents are the precipitatedsilicas. Precipitated silicas are obtained by precipitation of silicafrom dilute alkali metal silicate solutions by addition of strong acidsunder conditions where aggregation to the sol and gel cannot occur.Suitable processes for the production of precipitated silicas aredescribed, for example, in DE-OS 25 22 486 and in DE-OS 31 14 493.Preferred precipitated silicas are, for example, those which have a meanparticle size of 5 to 20 μm, a sieve residue (45 μm) of less than 1% byweight and a specific surface (BET) of 100 to 300 m²/g.

By virtue of the special combination of polishing agents, thedentifrices according to the invention have an excellent cleaningeffect, even against discoloration of the teeth by tea and nicotine. Atthe same time, a good polishing effect (smoothing of roughness) isobtained despite only moderate dentin and enamel abrasion. In spite ofthe presence of a relatively hard polishing component, namely aluminiumoxide, the dentifrices according to the invention have hardly anyscratching effect.

A preferred aluminium oxide polish is a lightly calcined alumina with acontent of at least 10% by weight of α-aluminium oxide of variousso-called γ-aluminium oxide modifications.

Suitable lightly calcined aluminas are prepared by calcination fromaluminium hydroxide. Aluminium hydroxide is converted by calcinationinto α-Al₂O₃ which is thermodynamically stable at temperatures above1200° C. The thermodynamically unstable Al₂O₃ modifications occurring attemperatures of 400 to 1000° C are known as γ-forms (cf. Ullmann,Enzyclopädie der technischen Chemie, 4th Edition (1974), Vol. 7, page298). The degree of calcination, i.e. the conversion into thethermodynamically stable α-Al₂O₃, can be adjusted as required throughthe choice of the temperature and the duration of the calcinationprocess. Light calcination gives an alumina with a γ-Al₂O₃ content whichis lower, the higher the calcination temperature and the longer thecalcination time. Lightly calcined aluminas differ from pure α-Al₂O₃ inthe lower hardness of the agglomerates, in a larger specific surface andlarger pore volumes.

The dentin abrasion (RDA) of the relatively lightly calcined aluminas tobe used in accordance with the invention containing 10 to 50% by weightof γ-Al₂O₃ is only 30 to 60% of the dentin abrasion of a heavilycalcined, pure α-Al₂O₃ (as measured in a standard toothpaste containing20% by weight alumina as sole polishing agent).

In contrast to α-Al₂O₃, γ-Al₂O₃ can be dyed red with anaqueous-ammoniacal solution of Alizarin S(1,2-dihydroxy-9,10-anthraquinone-4-sulfonic acid). The degree ofdyeability can be used as a measure of the degree of calcination orrather the percentage content of δ-Al₂O₃ in a calcined alumina:

Ca. 1 g Al₂O₃, 10 ml of a solution of 2 g/l Alizarin S in water and 3drops of an aqueous 10% by weight solution of NH₃ are introduced into atest tube and briefly boiled. The Al₂O₃ is then filtered off, washed,dried and examined under a microscope or evaluated by colorimetry.

Suitable lightly calcined aluminas containing 10 to 50% by weightγ-Al₂O₃ can be colored pale to deep pink by this method.

Aluminium oxide polishing agents with various degrees of calcination,fineness and bulk densities are commercially obtainable, for example the“Poliertonerden (polishing aluminas)” of Giulini-Chemie and ALCOA.

A particularly suitable quality “Poliertonerde P10 feinst” has anagglomerate size below 20 μm, a mean primary crystal size of 0.5 to 1.5μm and a bulk density of 500 to 600 g/l.

Sorbitol, xylitol, glycerol, propylene glycol or mixtures of thesepolyols may be present as humectants. Polyethylene glycols withmolecular weights of 400 to 2000 may also be partly present as humectantcomponents. Sorbitol in a quantity of 20 to 40% by weight is preferablypresent as the humectant.

The condensed phosphates are present in the form of their alkali metalsalts, preferably their sodium or potassium salts. The aqueous solutionsof these phosphates show an alkaline reaction on account of hydrolyticeffects. The dentifrices according to the invention are adjusted to a pHof 7.5 to 9 by addition of an acid. Suitable acids are, for example,citric acid, phosphoric acid or acidic salts, for example NaH₂PO₄.However, acidic salts of the condensed phosphates, i.e. for exampleK₂H₂P₂O₇, may also be partly used to adjust the dentifrice to therequired pH value.

Mixtures of various condensed phosphates or hydrated salts of thecondensed phosphates may also be used. However, the specified quantitiesof 2 to 12% by weight are based on the water-free salts. A sodium orpotassium tripolyphosphate in a quantity of 5 to 10% by weight of thecomposition is preferably present as the condensed phosphate.

The cleaning effect of the dentifrices according to the invention may befurther improved by addition of a suitable surfactant. The addition of asurfactant may also be desirable for producing a foam during brushing ofthe teeth, for stabilizing the dispersion of polishing agents and foremulsifying or solubilizing the flavoring oils. Suitable surfactantswhich develop a certain foaming effect are the nonionic surfactants, forexample sodium alkyl sulfates containing 12 to 18 carbon atoms in thealkyl group. These surfactants also have a certain enzyme-inhibitingeffect on the bacterial metabolism of plaque. Other suitable surfactantsare alkali metal salts, preferably sodium salts, of alkyl polyglycolether sulfate containing 12 to 16 carbon atoms in the linear alkyl groupand 2 to 6 glycol ether groups in the molecule, of linear alkane(C₁₂₋₁₈) sulfonate, of sulfosuccinic acid monoalkyl (C₁₂₋₁₈) esters, ofsulfated fatty acid monoglycerides, sulfated fatty acid alkanolamides,sulfoacetic acid alkyl (C₁₂₋₁₆) esters, acyl sarcosines, acyl tauridesand acyl isethionates containing 8 to 18 carbon atoms in the acyl group.

Zwitterionic and ampholytic surfactants may also be used, preferably incombination with anionic surfactants. However, it is particularlypreferred to use nonionic surfactants to promote the cleaning effect.Suitable nonionic surfactants are, for example, products of the additionof ethylene oxide with fatty alcohols, with fatty acids, with fatty acidmonoglycerides, with sorbitan fatty acid monoesters or with methylglucoside fatty acid monoesters. The quantity of ethylene oxide added onshould be so large that the surfactants are soluble in water, i.e. atleast 1 g/l should be soluble in water at 20° C. Another group ofsuitable surfactants are the alkyl (oligo)glycosides containing 8 to 16carbon atoms in the alkyl group and having a degree of oligomerizationof the glycoside unit of 1 to 4. Alkyl (oligo)glycosides, theirproduction and use as surfactants are known, for example, from U.S. Pat.No. 3,839,318, DE-A-20 36 472, EP-A-77 167 or WO-A-93/10132.

So far as the glycoside unit is concerned, monoglycosides (x=1) where amonosaccharide unit is attached to a C₁₀₋₁₆ fatty alcohol by a glycosidelinkage and oligomeric glycosides with a degree of oligomerization x ofup to 10 are suitable. The degree of oligomerization is a statisticalmean value on which the homolog distribution typical of such technicalproducts is based.

A particularly suitable alkyl (oligo)glycoside is an alkyl(oligo)glucoside with the formula RO(C₆H₁₀O)_(x)—H, where R is an alkylgroup containing 12 to 14 carbon atoms and x has a mean value of 1 to 4.

A nonionic solubilizer from the group of surface-active compounds may benecessary, particularly for solubilizing the generally water-insolubleflavoring oils. Particularly suitable nonionic solubilizers are, forexample, ethoxylated fatty acid glycerides, ethoxylated fatty acidsorbitan partial esters or fatty acid partial esters of glycerol orsorbitan ethoxylates. Solubilizers from the group of ethoxylated fattyacid glycerides include above all products of the addition of 20 to 60moles of ethylene oxide onto monoand diglycerides of linear fatty acidscontaining 12 to 18 carbon atoms or onto glycerides of hydroxy fattyacids, such as hydroxystearic acid or ricinoleic acid. Other suitablesolubilizers are ethoxylated fatty acid sorbitan partial esters, i.e.preferably products of the addition of 20 to 60 moles ethylene oxideonto sorbitan monoesters and sorbitan diesters of fatty acids containing12 to 18 carbon atoms. Other suitable solubilizers are fatty acidpartial esters of glycerol or sorbitan ethoxylates, i.e. preferablymonoesters and diesters of C₁₂₋₁₈ fatty acids and products of theaddition of 20 to 60 moles ethylene oxide onto 1 mole glycerol or onto 1mole sorbitol.

The dentifrices according to the invention preferably contain productsof the addition of 20 to 60 moles ethylene oxide onto hydrogenated ornon-hydrogenated castor oil (i.e. onto hydroxystearic acid or ricinoleicacid triglyceride), onto glycerol monostearate and/or distearate or ontosorbitan monostearate and/or distearate as solubilizers for anyflavoring oils present.

Suitable flavoring components are, for example, sweeteners and/orflavoring oils. Suitable flavoring oils are any of the natural andsynthetic flavors typically used in oral and dental care preparations.Natural flavors may be used both in the form of the essential oilsisolated from the drugs and in the form of the individual componentsisolated therefrom. The dentifrice should preferably contain at leastone flavoring oil from the group consisting of peppermint oil, spearmintoil, anise oil, Japanese anise oil, caraway oil, eucalyptus oil, fenneloil, cinnamon oil, clove oil, geranium oil, sage oil, pimento oil, thymeoil, marjoram oil, basil oil, citrus oil, gaultheria oil or one or morecomponents of these oils isolated from them or synthetically produced.The most important components of the oils mentioned are, for example,menthol, carvone, anethol, cineol, eugenol, cinnamaldehyde,caryophyllene, geraniol, citronellol, linalool, salvia, thymol,terpinene, terpineol, methyl chavicol and methyl salicylate. Othersuitable flavors are, for example, menthyl acetate, vanillin, ionone,linalyl acetate, rhodinol and piperitone.

In addition, the dentifrices according to the invention may contain atherapeutic agent for controlling caries, scale, parodontitis or otherdiseases of the mouth and teeth. An active principle preferably presentis a caries-inhibiting fluorine compound, preferably from the group offluorides or monofluorophosphates in a quantity of 0.1 to 0.5% by weightfluorine. Suitable fluorine compounds are, for example, sodium fluoride,potassium fluoride, tin fluoride, sodium monofluorophosphate (Na₂PO₃F),potassium monofluorophosphate or the fluoride or an organic aminocompound.

Other suitable therapeutic agents are, for example scale inhibitors, forexample organophosphates, such as 1-azacycloheptane-2,2-diphosphonicacid (Na salt) or 1-hydroxyethane-1,1-diphosphonic acid (Na salt), andantimicrobial plaque inhibitors such as, for example, hexachlorophene,chlorhexidine, hexetidine, triclosan, bromochlorophene, phenylsalicylate. Substances effective in promoting remineralization and theclosure of dental lesions, for example dicalcium phosphate dihydrate,preferably in combination with magnesium ions, may also be present inthe dentifrices according to the invention.

In one preferred embodiment, the toothpastes according to the inventionadditionally contain, for example, 1 to 10% by weight of dicalciumphosphate dihydrate (brushite) and 0.1 to 0.5% by weight of magnesiumions, preferably in the form of a water-soluble magnesium salt, forexample magnesium sulfate, magnesium fluoride or magnesiummonofluoro-phosphate.

Finally, the toothpastes according to the invention may contain othercomponents which are normally encountered in dentifrices and which donot reduce the effects according to the invention. Such typicaltoothpaste additives are, for example,

other polishing agents in relatively small quantities of, for example, 1to 10% by weight, for example calcium carbonate (chalk), insolublesodium metaphosphate, calcium pyrophosphate, hydroxyl apatite, aluminiumhydroxide, sodium aluminium silicates (zeolite A) or particulate organicpolymers, for example polymethacrylate,

pigments, for example titanium dioxide or zinc oxide,

dyes,

pH regulators and buffers, for example sodium citrate or sodiumbicarbonate, sodium benzoate,

wound-healing and anti-inflammatory agents such as, for example,allantoin, urea, panthenol, azulene or camomile extract,

preservatives such as, for example, sorbic acid salts, p-hydroxybenzoicacid ester.

The following Examples are intended to illustrate the invention.

EXAMPLES

The following toothpastes were prepared:

Composition 1 2 3 4 5 Sident 8 (1) 14.0 — — — — Sorbosil AC 39 (2) —14.0 — — 14.0 Zeodent 113 (3) — — 14.0 — — Zeodent 623 (4) — — — 14.0 —Poliertonerde P10 feinst (5) 1.0 1.0 1.0 1.0 0.5 Na₅P₃O₁₀ 5.0 5.0 5.05.0 5.0 (Na tripolyphosphate) Na₂PO₃F — 0.8 — — — (Namonofluorophosphate) NaF 0.24 — 0.24 0.24 0.24 Na saccharinate 0.1 0.10.1 0.1 0.1 Titanium dioxide 0.5 0.5 0.5 0.5 0.5 PHB methyl ester 0.10.1 0.1 0.1 0.1 Carboxymethyl cellulose 1.25 1.25 1.25 1.25 1.25Sorbitol (70%) 32.0 32.0 32.0 32.0 32.0 1,2-Propylene glycol 5.0 5.0 5.05.0 5.0 Cremophor RH 60 (7) 1.0 — 1.0 1.0 1.0 Arlatone289 (8) — 1.0 — —— Flavoring oil 0.8 0.8 0.8 0.8 0.8 Water to to to to to 100 100 100 100100 Composition 6 C1 C2 C3 Sorbisil AC 39 (2) 14 14 14 14 PoliertonerdeP 10 feinst (5) 1 — — — Precarb 100 (6) — 2 2 2 Na₅P₃O₁₀ 10 10 5 0Na₂PO₃F 0.8 0.8 0.8 0.8 NaF — — — — Na saccharinate 0.1 0.1 0.1 0.1Titanium dioxide 0.5 0.5 0.5 0.5 PHB methyl ester 0.1 0.1 0.1 0.1Carboxymethyl cellulose 1.25 1.25 1.25 1.25 Sorbitol (70%) 32.0 32.032.0 32.0 1,2-Propylene glycol 5.0 5.0 5.0 5.0 Arlatone 289 (8) 1.0 1.01.0 1.0 Flavoring oil 0.8 0.8 0.8 0.8 Water to 100 to 100 to 100 to 100The following commercial products were used: (1) Sident ® 8 silicapolish (DEGUSSA) mean particle size: 10.0 μm sieve residue (45 μm):≦0.3% compacted bulk density: 300 g/l (2) Sorbosil AC 39 silica polish(Crosfield Ltd.) particle size: 9-13 μm (3) Zeodent 113 silica polish(Huber Chemicals) mean particle size: 12 μm sieve residue (45 μm): 1.0%max. spec. surface (BET): 150 m²/g (4) Zeodent 623 silica polish (HuberChemicals) mean particle size: 12 μm sieve residue (45 μm): 0.5% max.spec. surface (BET): 250 m²/g (5) Poliertonerde P10 feinst aluminiumoxide polish (Giulini Chemie) mean agglomerate size: <20 μm (min. 99%)primary particle size: ca. 1 μm degree of calcination: low (6) Precarb100 calcium carbonate (chalk) compacted bulk density 0.5 g/ml spec.surface: 9.0 m²/g (7) Cremophor RH 60 hydr. castor oil + 60 moles EO (8)Arlatone 289 hydr. castor oil + 54 moles EO melting point: 39° C. HLBvalue: 14.4

Determination of the cleaning effect (CRS)

Method

The surface of bovine teeth was conditioned, stained with tea underdefined conditions and cleaned with the toothpaste to be tested underdefined conditions. The lightening in color obtained was measured bycolorimetry and was compared with the lightening effect of a standardtoothpaste.

Sample Preparation

Bovine incisors were cut into 7×7 mm blocks which were then mounted withwax on Plexiglas squares (1×2.5×2.5 cm) in such a way that only theenamel surface was exposed. The enamel surface was polished until itappeared uniformly smooth.

Sample Conditioning

The mounted tooth blocks were successively immersed in 0.12 Nhydrochloric acid (60 seconds), saturated Na₂CO₃ solution (120 seconds)and in 1% phytic acid solution (60 seconds). After each treatment, thesamples were rinsed with deionized water and dried by blotting withabsorbent paper. The tooth samples were then fixed to the stainingapparatus and moved for 5 days through a solution of black tea at 20° C.The tea solution had been prepared by extracting a 1.5 g teabag with 300g of boiling water (10 minutes) and was renewed twice a day.

Polishing Tests

The mounted tooth blocks were then placed in a Grabenstetter V8 brushingmachine and were brushed in a toothpaste suspension of 20 g paste and 40g deionized water using a soft Oral-B toothbrush (pressure applied 150g). A suspension of 10 g of calcium pyrophosphate in 50 g of swollencarboxymethyl cellulose (0.5% CMC, 10% glycerol, 89.5% water) was usedas the polishing standard. The cleaning effect of this standard isdefined as the 100% value.

Measurement of the Cleaning Effect

The lightening effect was measured to DIN 5033 using a Dr. Lange colordifference measuring instrument (type Micro Color (DC 8334)). A xenonlamp producing D 65 standard light corresponding to daylight was used.Barium sulfate was used as the color standard.

Double measurements of a circular area 7 mm in diameter on the samplesurface were carried out. Eight stained tooth samples were used for eachtoothpaste and average values were formed. The test parameter used wasthe standard color value Y determined to DIN 5033 which is a measure ofthe lightness of a color.

Lightness measurement was carried out after 1000 brush strokes. Thecleaning effect CRS (cleaning ratio soft) is calculated as follows:${{CRS}\quad\lbrack\%\rbrack} = {\frac{{\text{average standard color value}\text{Y}} - \text{increment test paste}}{{\text{average standard color value}\text{Y}} - \text{increment polishing standard}} \cdot {100\quad\lbrack\%\rbrack}}$

Determination of Abrasiveness (RDA)

Abrasiveness was determined by the RDA method (radioactive dentinabrasion) using the Grabenstetter process of Missouri AnalyticalLaboratories, St. Louis, Mo. (cf. J. Dent. Res. 17, 1060-1068 (1958).

Results

Example 1 2 3 4 5 6 C1 C2 C3 CRS % 90 88 103 98 73 97 80 64 31 RDA %n.d.* 66 55 95 69 n.d. n.d. 57 n.d. (*n.d. not determined)

The results show that, without aluminium oxide (C1-C3), a weakercleaning effect is obtained than with the toothpastes according to theinvention (1-4), despite high Na tripolyphosphate contents (C1), andthat dentin abrasion shows hardly any increase in relation to thecomparison pastes despite the high cleaning performance.

What is claimed is:
 1. A dentifrice in the form of anqueous paste orliquid dispersion, comprising (a) 10% to 30% by weight of a combinationof one or more silica polishing agents and aluminum oxide in a ratio byweight of 10:0.2 to 10:2, said aluminum oxide comprising at least 10% byweight of γ-aluminum oxide, based on the total weight of said aluminumoxide; (b) 20% to 50% by weight of a humectant selected from the groupconsisting of sorbitol, glycerol, 1,2-propylene glycol, polyethyleneglycols, and mixtures thereof; and (c) 2% to 12% by weight of acondensed phosphate selected from the group consisting oftripolyphosphate, pyrophosphate, trimetaphosphate, and mixtures thereof,said condensed phosphates being in the form of an alkali metal orammonium salt, wherein the percentages of the combination of the silicapolishing agent and aluminum oxide, the humectant and the condensedphosphate are based on the total weight of the composition.
 2. Thedentifrice of claim 1, wherein the aluminum oxide comprises lightlycalcined alumina containing 10% to 50% by weight of γ-aluminum oxide. 3.The dentifrice of claim 1, comprising 25% to 40% by weight of sorbitol.4. The dentifrice of claim 2, comprising 25% to 40% by weight ofsorbitol.
 5. The dentifrice of claim 1, comprising 5% to 10% by weightof sodium or potassium tripolyphosphate.
 6. The dentifrice of claim 2,comprising 5% to 10% by weight of sodium or potassium tripolyphosphate.7. The dentifrice of claim 4, comprising 5% to 10% by weight of sodiumor potassium tripolyphosphate.
 8. The dentifrice of claim 1, wherein thesilica polishing agents comprise precipitated silica with a particlesize of 5 to 20 μm and a specific surface of 100 to 300 g/l.
 9. Thedentifrice of claim 7, wherein the silica polishing agents compriseprecipitated silica with a particle size of 5 to 20 μm and a specificsurface of 100 to 300 g/l.
 10. The dentifrice of claim 1, comprising0.1% to 0.5% by weight of fluorine.
 11. The dentifrice of claim 2,comprising 0.1% to 0.5% by weight of fluorine.
 12. The dentifrice ofclaim 4, comprising 0.1% to 0.5% by weight of fluorine.
 13. Thedentifrice of claim 9, comprising a fluoride or monofluorophosphatessuch that the dentifrice comprises 0.1% to 0.5% by weight of fluorine.